Field of the Invention
The present invention is directed in general to the field of packaged integrated circuit devices. In one aspect, the present invention relates to an improved packaging scheme for producing integrated circuits with reduced delamination.
Description of the Related Art
Microchips are formed from a variety of dissimilar materials. A semiconductor die, formed from silicon, gallium arsenide, germanium, or some other semiconductor material, may be attached to the flag portion of a lead frame and/or heatsink which may be formed with copper or some other thermally conductive material. The semiconductor die is bonded to the die flag with an adhesive material or structure, such as a die bond soldering compound. In selected Quad Flat No-Lead (QFN) packages, the lead frame includes a series of lead contacts that serve as the output electrical contacts for the microchip. To electrically couple the semiconductor die to the lead frame, metal wires extend between the semiconductor die and the lead contacts. To protect the semiconductor die, wires, and lead contacts, a plastic mold compound encapsulates the semiconductor package.
A common problem with integrated circuit packages, such as power QFN (PQFN) and small outline integrated circuit (SOIC) power packages, is delamination of the mold compound from the region surrounding the die on the die attach flag(s), and other lead frame regions. This problem is particularly acute with SOICs that use certain types of organic polymer-based die attach adhesives due to the bleed of liquid material from the die attach adhesive onto the surface of the flag surrounding the die. Delamination also occurs with PQFN packages which use solder die attach for the high power die. Mold compound delamination often leads to electrical problems due to variation in the drain-source on-state resistance (Rdson) and compensation series resistance (CSR), and can also result in separation in the die attach region (die to solder, die to organic polymer adhesive, solder or adhesive to lead frame) in portions of the die attach interface. While the previous descriptions refer to lead frame-based packages, delamination of the encapsulation material from conductor regions on the surface of a printed circuit board-based (PCB) package, also referred to as an organic package, may also be a problem.